dhcp運作時需要指定一個pool給它（可分發的網段區間）
並設定希望指派的設定（ip mask getway lifetime等等）
當使用者開啟電腦後
若主機網路設定是dhcp
則會以廣播方式詢問dhcp伺服器在哪
找到之後向它發出要求
dhcp server若還有可用ip
則會以租約方式將設定租給該電腦並留下紀錄
如此一來該主機便會設定管理者希望的網路規劃
而不需要使用者或是管理者手動指派
而管理員只要在dhcp server即可得知所有電腦ip及租約情況
當然dhcp也可以紀錄主機MAC以指派固定ip
dhcp server在公司是很重要的服務
否則管理員就要手動為每一台主機設定
變更ip時也只好一台一台更改
dhcp所提供的服務還不只些而已
實際上依公司或環境運作需求
可以作更多樣化的設定
想更瞭解可以看看wiki或google
畢竟我在這能說的也只是極少部份
我拿以下幾台來做比較
1. 168.95.1.1 Hinet DNS
2. 198.153.192.1 Norton DNS
3. 8.8.8.8 Google DNS
4. 210.208.81.3 某上市公司DNS
1.ping 168.95.1.1
Pinging 168.95.1.1 with 32 bytes of data:
Reply from 168.95.1.1: bytes=32 time=29ms TTL=249
Reply from 168.95.1.1: bytes=32 time=29ms TTL=249
Reply from 168.95.1.1: bytes=32 time=29ms TTL=249
Reply from 168.95.1.1: bytes=32 time=29ms TTL=249
dig @168.95.1.1 www.mobile01.com
; <<>> DiG 9.2.3 <<>> @168.95.1.1 www.mobile01.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1
;; QUESTION SECTION:
;www.mobile01.com. IN A
;; ANSWER SECTION:
www.mobile01.com. 6463 IN A 211.75.83.3
;; AUTHORITY SECTION:
mobile01.com. 855 IN NS dns2.mobile01.com.
;; ADDITIONAL SECTION:
dns2.mobile01.com. 2516 IN A 211.75.83.25
;; Query time: 43 msec
;; SERVER: 168.95.1.1#53(168.95.1.1)
;; WHEN: Wed Sep 01 14:43:23 2010
;; MSG SIZE rcvd: 85
2.ping 198.153.192.1
Pinging 198.153.192.1 with 32 bytes of data:
Reply from 198.153.192.1: bytes=32 time=248ms TTL=44
Reply from 198.153.192.1: bytes=32 time=259ms TTL=44
Reply from 198.153.192.1: bytes=32 time=242ms TTL=44
Reply from 198.153.192.1: bytes=32 time=242ms TTL=44
Ping statistics for 198.153.192.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 242ms, Maximum = 259ms, Average = 247ms
dig @198.153.192.1 www.mobile01.com
; <<>> DiG 9.2.3 <<>> @198.153.192.1 www.mobile01.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.mobile01.com. IN A
;; ANSWER SECTION:
www.mobile01.com. 11658 IN A 211.75.83.3
;; Query time: 234 msec
;; SERVER: 198.153.192.1#53(198.153.192.1)
;; WHEN: Wed Sep 01 14:45:58 2010
;; MSG SIZE rcvd: 50
3.ping 8.8.8.8
Pinging 8.8.8.8 with 32 bytes of data:
Reply from 8.8.8.8: bytes=32 time=31ms TTL=55
Reply from 8.8.8.8: bytes=32 time=31ms TTL=55
Reply from 8.8.8.8: bytes=32 time=30ms TTL=55
Reply from 8.8.8.8: bytes=32 time=30ms TTL=55
Ping statistics for 8.8.8.8:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 30ms, Maximum = 31ms, Average = 30ms
dig @8.8.8.8 www.mobile01.com
; <<>> DiG 9.2.3 <<>> @8.8.8.8 www.mobile01.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.mobile01.com. IN A
;; ANSWER SECTION:
www.mobile01.com. 1601 IN A 211.75.83.3
;; Query time: 46 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Sep 01 14:47:24 2010
;; MSG SIZE rcvd: 50
4.ping 210.208.81.3
Pinging 210.208.81.3 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 210.208.81.3:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
dig @210.208.81.3 www.mobile01.com
; <<>> DiG 9.2.3 <<>> @210.208.81.3 www.mobile01.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0
;; QUESTION SECTION:
;www.mobile01.com. IN A
;; ANSWER SECTION:
www.mobile01.com. 977 IN A 211.75.83.3
;; AUTHORITY SECTION:
mobile01.com. 977 IN NS dns.mobile01.com.
mobile01.com. 977 IN NS dns2.mobile01.com.
;; Query time: 73 msec
;; SERVER: 210.208.81.3#53(210.208.81.3)
;; WHEN: Wed Sep 01 14:54:04 2010
;; MSG SIZE rcvd: 87
個人得到的結論:
利用Ping dns不一定就能完全決定dns是否比較快 or慢
重點還是在query回應的速度比較重要
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